﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp4
{
    class Program
    {
        static void Main(string[] args)
        {
            string a;
            Console.WriteLine("请输入半径");
            a = Console.ReadLine();
            double r = double.Parse(a);
            double num = 3.14 * (r* r);
            Console.WriteLine(num);
        }
    }
}
